Roman to Integer

public class Solution {
    public int romanToInt(String s) {
        int result = 0;
        if(s == null || s.length() == 0){
            return result;
        }
        
        for(int i = 0; i< s.length(); i++){
            if(i > 0 && cToI(s.charAt(i)) > cToI(s.charAt(i-1))){
                // IV(4) result = 1 + 5 - 1*2 = 4
                result += cToI(s.charAt(i)) - cToI(s.charAt(i-1))*2;
            }else{
                result += cToI(s.charAt(i));
            }
        }
        
        return result;
    }
    
   private static int cToI(char c) {
        switch (c) {
        case 'I':
            return 1;
        case 'V':
            return 5;
        case 'X':
            return 10;
        case 'L':
            return 50;
        case 'C':
            return 100;
        case 'D':
            return 500;
        case 'M':
            return 1000;
        default:
            return 0;
        }
    }
}